1. Field of the Invention
The present invention relates to a vacuum pump including two one-or multi-stage gas friction pumps and a multi-stage pump arranged downstream of the gas friction pumps.
2. Description of the Prior Art
For producing high vacuum, combinations of different types of vacuum pumps are necessary because a wide pressure region between atmospheric pressure and pressure of about 10xe2x88x924 mbar and lower includes several flow regions in which the physical characteristics and conditions of gas flows are governed by different laws.
For producing a high vacuum, at least two vacuum pumps having different designs and operational characteristics are combined on a common stand. Known are stands which include a turbomolecular pump, which is used as a high vacuum pump, and a vane-type rotary pump which discharges against atmospheric pressure. Pump stands, which consist of at least two vacuum pumps, necessary for achieving the required vacuum-technical parameters, such as pressure ratio and suction capacity, are expensive and occupy a large space. Each pump requires its own drive, power supply, control means, and bearing system. Connection conduits, which connect the pumps and are provided with necessary valves, increase the costs of such pump stands.
Accordingly, an object of the present invention, is to provide a vacuum pump having a compact structure so that the above-discussed drawbacks of pump stands formed of several pumps, are eliminated.
Another object of the present invention is to provide an integral vacuum pump encompassing the entire pressure region between atmospheric pressure and pressure of about 10xe2x88x924 mbar and lower.
A further object of the present invention is to provide a vacuum pump having sufficiently high pressure ratio and a suction capacity capable to meet the requirements of practical applications of a vacuum pump.
Yet another object of the present invention is to provide a vacuum pump having reliable operational characteristics.
Yet an additional object of the present invention is to provide a vacuum pump the high-vacuum side of which is lubrication-free.
These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a vacuum pump including a common suction region, two gas friction pumps arranged parallel to each other and having each at least one stage having its inlet communicating with the common suction region and its outlet communicating with a separate discharge region, a multi-stage pump arranged downstream of the two gas friction pumps and having a suction chamber, connection conduits for communicating the separate discharge region with a common discharge chamber, and a conduit for communicating the common discharge chamber with the suction chamber of the multi-stage pump. With such an arrangement, an aspirated gas stream is separated into two streams flowing each through an associated gas friction pump into a respective discharge region, with the streams from both discharge regions being combined in a common stream flowing into a common discharge chamber from which a combined stream flows into the suction chamber of the multi-stage pump, with the gas being further compressed in the multi-stage pump.
A vacuum pump according to the present invention has a compact construction and covers the entire pressure region from atmospheric pressure up to the high vacuum region. The parallel arrangement of the gas friction pumps on the high-vacuum side provides a double-flow region that insures a high suction capacity. In the gas friction pumps, the aspirated gas is sufficiently compressed, so that in the downstream pump only a single-flow gas stream is necessary. This combination, together with combining output flows of both gas friction pumps in a single flow delivered into the suction chamber of the following stage, provides for a compact structure, with a noticeable decrease in overall dimensions and with reduction in construction costs. The foregoing arrangement of pumps permits to arrange the bearing on opposite sides of the rotor shaft, which insures a stable support and permits to use bearing having a smaller diameter. A stable support insures a problem-free drive with a high rotational speed. In addition, the gas friction pumps separate the bearings from the high-vacuum side, which prevents the lubrication medium from reaching the high vacuum side.
This arrangement and the operating method favors formation of the gas friction pumps as Holweck pumps. Forming the gas friction pumps as Holweck pumps permits to obtain a maximal pressure ratio in a narrow space. The double-flow arrangement permits to obtain a necessary suction capacity.
As a multi-stage, downstream pump advantageously a regenerative pump is used. The regeneration pump compresses the gas, which is discharged by two gas friction pumps, to atmospheric pressure. With a high gas yield, any intermediate stage of the regenerative pump, except the stage adjacent to the atmospheric pressure, can be directly connected with the gas outlet flange by a connecting conduit. In this case, large amounts of gas need not be pumped through the geometrically small end stages leading to increase of time in which the gas is delivered to the gas outlet flange. When the amount of gas is small, the conduit is closed by a pressure relief valve, and compression to atmospheric pressure is effected in last stages. However, the present invention is not limited to use of a regenerative pump. Other pumps, which discharge against atmosphere can be used.
A big advantage of the regenerative pump consists in that its stator elements are formed, according to the present invention, as undivisible discs. In conventional constructions, in which divided discs are mounted between the rotor discs, a back flow through the formed gaps can take place, which leads to losses and the reduction of the pressure ratio. Using undivisible discs eliminates back flow. The uses of undivisible stator elements, however, is only possible when the rotor elements are secured on the rotor shaft, according to the present invention, with clamping rings. Only in this case, the rotor and stator elements can be alternatively mounted one behind the other, with maintaining of an optimal axial gap therebetween.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of the preferred embodiment, when read with reference to accompanying drawing.